1. Field of the Invention
The present invention relates to a vacuum pump having an exhaust assembly for evacuating gas through an interaction between a rotor and a stator, and more particularly to a vacuum pump which is capable of operating in a wide operation range by preventing reaction products produced by a process gas from being precipitated inside the pump in a high pressure region on an exhaust port side.
2. Description of the Related Art
One conventional vacuum pump in the form of a turbo-molecular pump is shown in FIG. 7 of the accompanying drawings. As shown in FIG. 7, the turbo-molecular pump has an exhaust assembly comprising a turbine blade exhaust section L1 and a thread groove exhaust section L2 each jointly made up of a rotor R and a stator S which are housed in a cylindrical pump casing 1. The pump casing 1 has a lower portion covered with a pump base 2 to which there is connected an exhaust port member 21 having an exhaust port 20 communicating with an exhaust region of the thread groove exhaust section L2. The pump casing 1 has an intake port 1a defined in an upper portion thereof which has a flange 1b for connection to a device or a pipe to be evacuated. The stator S mainly comprises a stationary cylindrical sleeve 3 erected centrally in the pump base 2 and stationary components of the turbine blade exhaust section L1 and the thread groove exhaust section L2.
The rotor R comprises a main shaft 4 inserted coaxially in the stationary cylindrical sleeve 3 and a rotary cylindrical sleeve 5 mounted on the main shaft 4. Between the main shaft 4 and the stationary cylindrical sleeve 3, there are disposed a drive motor 6 and an upper radial bearing 7 and a lower radial bearing 8 which are positioned respectively above and below the drive motor 6. An axial bearing 11 is disposed at a lower portion of the main shaft 4, and comprises a target disk 9 mounted on the lower end of the main shaft 4, and upper and lower electromagnets 10a, 10b provided on the stator S side. The electromagnets 10a, 10b are disposed respectively above and below the target disk 9. By this magnetic bearing system, the rotor R can be rotated at a high speed under 5-axis active control.
The rotary cylindrical sleeve 5 has rotary blades 12 integrally disposed on its upper outer circumferential region. In the pump casing 1, there are provided stator blades 13 disposed axially alternately interdigitating relation to the rotary blades 12. The rotary blades 12 and the stator blades 13 jointly make up the turbine blade exhaust section L1 which evacuates the gas by way of an interaction between the rotary blades 12 that rotates at a high speed, and the stator blades 13 that remain stationary. The stator blades 13 are secured in position with their circumferential edges vertically held by stator blade spacers 14.
The thread groove exhaust section L2 are positioned beneath the turbine blade exhaust section L1. The rotary cylindrical sleeve 5 has a thread groove barrel 18 disposed around the stationary cylindrical sleeve 3 and having thread grooves 18a on its outer circumferential surface. The stator S has a thread groove spacer 19 surrounding the thread groove barrel 18. The thread groove exhaust section L2 evacuates the gas by way of a dragging action of the thread grooves 18a of the thread groove barrel 18 which rotates at a high speed.
With the thread groove exhaust section L2 disposed downstream of the turbine blade exhaust section L1, the turbo-molecular pump is of the wide range type capable of handling a wide range of rates of gas flows. In the conventional turbomolecular pump shown in FIG. 7, the thread grooves 18a of the thread groove exhaust section L2 are defined in the rotor R side. However, the thread grooves of the thread groove pumping section L2 may be defined in the stator S side.
The turbo-molecular pump may be used with a semiconductor fabrication facility. In such an application, when a process gas is drawn from the intake port 1a and discharged from the exhaust port 20, reaction products produced by the process gas tend to be precipitated in the exhaust passage on the exhaust port 20 side which is held under a high pressure, clogging the gap between the rotor R and the stator S or forming deposits on the rotor R. The rotor R is then liable to be brought out of balance and rotate unstably, and possibly locked against rotation, causing a pump failure, when things come to the worst. If the reaction products are deposited until they close the exhaust passage, then the pump undergoes an undue internal pressure buildup, which may prevent the pump from providing a sufficient exhausting capability and may pose an excessive load on the drive motor, resulting in a pump failure.
Various reaction products are formed depending on the process gas used. One typical reaction product is aluminum chloride (AlCl3) that is produced when aluminum is etched. FIG. 8 of the accompanying drawings shows a vapor pressure curve of aluminum chloride. It can be seen from FIG. 8 that aluminum chloride tends to go into a solid phase and become easily solidified in a region where the temperature is low and the partial pressure is high. Because of such a property of aluminum chloride, the gas which is being discharged by the turbo-molecular pump is solidified more easily in thread groove exhaust section L2 than the turbine blade exhaust section L1.
To avoid the above drawback, as shown in FIG. 7, a heater 15 is disposed around the pump casing 1 to transfer its heat to the thread groove spacer 19 to heat the thread groove exhaust section L2 to increase its temperature, and a heater 17 is disposed around the exhaust port member 21 to heat the exhaust port member 21 to increase its temperature.
In order to measure the temperatures increased by the heaters 15, 17 and control the turning on and off of these heaters 15, 17, temperature measuring means such as thermistors, thermocouples, etc. are disposed near the heaters 15, 17, i.e., near heater mounting portions of the pump casing 1 and the exhaust port member 21. These temperature measuring means measure atmospheric side temperatures of these heater mounting portions, and the measured atmospheric side temperatures are used as feedback signals for temperature control.
In order to protect the bearings 7, 8, 11 which support the rotor R, the drive motor 6 which rotates the rotor R, and the entire rotor R against high temperatures achieved when the overall pump is heated, as shown in FIG. 7, a coolant pipe 23 is disposed between the pump base 2 and a lid 22, and a coolant flows through the coolant pipe 23 to cool the bearings 7, 8, 11, the drive motor 6, and the rotor R. The rotor (rotary blades), in particular, is made of an aluminum alloy having a high specific strength, and needs to keep its temperature below an allowable temperature because it has a low high-temperature strength and tends to suffer creeping, i.e., to be deformed while in operation at a high temperature under a high pressure over a long period of time. Generally, it has been customary to control the temperature in the pump by controlling the turning on and off of the heaters and controlling the opening and closing of a solenoid-operated valve (not shown) which is connected to the coolant pipe 23.
With the conventional vacuum pump, the heating means such as heaters are disposed outside of the pump in order to prevent reaction products from being precipitated due to the process gas in a relatively high pressure region in the exhaust passage, and the cooling means is also disposed outside of the pump to prevent the pump from suffering trouble due to high temperatures caused by the heating means. However, these conventional attempts are disadvantageous as follows:
For the purpose of preventing or reducing the precipitation of reaction products to increase the service life of the pump and the durability thereof, the high pressure region in the pump, i.e., on the exhaust port side of the exhaust passage, may be kept at a high temperature. On the other hand, if the problem of the precipitation of reaction products is ignored, then in order to protect a rotor (rotary blade) material which has to be used under a certain allowable stress and in an allowable temperature range, components and materials of the bearings which support the rotor, and components and materials of the drive motor which rotates the rotor, etc. from generation of heat or high temperature regions in the vacuum pump, and to keep those materials durable, these materials need to be isolated from the high temperature regions or need to be cooled if they cannot sufficiently be isolated from the high temperature regions.
Therefore, in order to keep the components of the vacuum pump durable and reduce or prevent the precipitation of reaction products, the region where the reaction products tend to be precipitated has to be held at a high temperature, and the region which needs to be kept in an allowable temperature range has to be isolated from the high temperature regions or cooled by the cooling means.
While the vacuum pump is in normal operation, a low pressure (vacuum) lower than the atmospheric pressure is developed in the pump, and the transfer of heat is blocked in the vacuum, resulting in a vacuum heat-insolating state. In such a vacuum heat-insolating state, when the heating means disposed outside of the pump transfers heat through pump components to increase the temperature of the exhaust passage in the pump, a large loss of heat, i.e., energy, is caused. Particularly, external pump components (casing and housing) that are exposed to the atmosphere produce a large amount of heat radiation, and they have a low heating efficiency. Internal pump components transfer heat possibly to the regions which are not to be heated, such as the bearings, the motor, and the turbine blade exhaust section. When the heat produced by the heaters disposed outside of the pump is transferred, a large amount of heat tends to be consumed, and the pump fails to save energy effectively. In addition, the heating means disposed outside of the pump is likely to be large in size, presenting an obstacle to efforts to make the overall pump compact.
When the temperature of regions in the pump is measured by the temperature measuring means disposed outside of the pump, similar to the heating means, via heat transfer, the temperature measuring means has a low temperature measuring response and accuracy.
It is therefore an object of the present invention to provide a vacuum pump which is capable of preventing reaction products produced by a process gas from being precipitated in the pump, of holding various pump components in an allowable temperature range, and hence of operating in a wide operation range, and which has increased durability.
To accomplish the above object, there is provided in accordance with the present invention a vacuum pump, comprising: a pump casing having an intake port and an exhaust port; an exhaust assembly disposed in the pump casing and having a rotor and a stator; and a heating unit for heating a stator side component of the exhaust assembly positioned near the exhaust port; wherein the heating unit is disposed in a space inside the pump casing where is evacuated to the vacuum, and held in contact with at least a portion of the stator side component of the exhaust assembly positioned near the exhaust port.
Since the heating unit is held in contact with at least a portion of a region in the pump which is to be heated, the region to be kept at a high temperature can directly be heated. The region can be heated with a very small amount of heat when it is heated in a vacuum heat-insolating state in which no heat is transferred to and from outside of the pump. Because the amount of heat escaping to a region (particularly outside of the pump) other than the region to be heated by way of heat transfer is reduced, the pump is an energy saver and is highly responsive to heating.
The vacuum pump further includes a bearing supporting the rotor, a motor for rotating the rotor, and a cooling unit for cooling at least one of the rotor, the bearing, and the motor.
By efficiently cooling these components, the performance and functions of the bearing and the motor can be maintained as desired. Since the rotor is generally disposed closely to the bearing and the motor, the effect of heat transfer to and from the rotor is large. Therefore, the rotor can efficiently be cooled by cooling the bearing and the motor, and can be kept in an allowable temperature range. As a result, the operation range of the vacuum pump can be increased.
The cooling unit should preferably be positioned as closely to the components to be cooled as much as possible for an increased cooling effect. The heat insulating and transferring regions having large heat capacity should preferably be provided to prevent the cooling effect from acting on an exhaust passage leading to the exhaust port side of the vacuum pump.
A vacuum pump includes a heat insulating member for thermally insulating an intake port side group and an outlet port side group of stator side components of the exhaust assembly from each other.
With the above arrangement, the temperature of the stator near the exhaust port where reaction products tend to be precipitated under high pressure is kept at a high level, and the temperature of the stator near the intake port where the heat is liable to be generated when the rotating rotor agitates the gas being discharged so that the transfer of heat from the rotor to the stator is accelerated to keep the rotor at a low temperature, eventually preventing reaction products from being precipitated and increasing the operation range of the vacuum pump. The heat insulating means, which includes a space such as a gap, may be disposed to separate the stator side components of the exhaust assembly from the pump base integrated the bearings and the motor so that the high temperature state of the stator side components of the exhaust assembly does not affect the bearings and the motor, and the rotor and the shaft positioned near the pump base, preventing the harmful effects by the high temperature.
The vacuum pump further includes a vacuum seal member for sealing a terminal lead-out portion of the heating unit.
The vacuum seal member is effective to prevent the vacuum in a lower pressure region (vacuum region) in the vacuum pump from being broken due to the heating unit disposed in the pump. The response of the vacuum pump to heating is increased, and the energy required by the heating unit is reduced. The vacuum seal member may be an elastic member such as an O-ring, an adhesive member of synthetic resin, or a welded combination of components. If the O-ring seal is used as the vacuum seal member, a vacuum seal recess, in which the vacuum seal member is disposed, may have a rectangular cross section or a triangular cross section from the standpoint of space saving.
The vacuum pump further includes a temperature measuring unit for measuring a temperature of the stator side component of the exhaust assembly positioned near the exhaust port; wherein the temperature measuring unit has a temperature measuring element disposed so as to be held in contact with the stator side component of the exhaust assembly positioned near the exhaust port.
The temperature measuring unit directly measures the temperature of the region which is heated, and hence can measure the temperature highly accurately and produce a measured value as a basis for good temperature control.
The vacuum pump further includes a vacuum seal member for sealing a terminal lead-out portion of the temperature measuring unit.
The vacuum seal member is effective to prevent the vacuum in a lower pressure region (vacuum region) in the vacuum pump from being broken due to the temperature measuring unit disposed in the pump. The response of the vacuum pump to heating can thus be increased.
The exhaust assembly comprises at least one of a turbine blade exhaust section and a thread groove exhaust section.
The exhaust assembly comprises the turbine blade exhaust section and a cooling unit for cooling the turbine blade exhaust section.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.